This invention relates to printing ink compositions having less than 5 percent by weight (wt. %) of volatile organic compounds (VOCs) and no hazardous air pollutants. More specifically, this invention relates to the use of glycerine in printing ink formulations to dissolve the resin, thereby reducing the need for employing VOCs.
VOCs are photoreactive chemicals that contain elemental carbon that can lead to ozone formation. In the printing ink industry, VOCs are used to control the properties of the printing ink. Each VOC is property specific. For example, an alcohol is used to decrease the drying time of an ink and a glycol would be used to increase the drying time of the same ink. These chemicals may also affect the printability properties of the ink such as lay, color, shade and strength, and rub resistance to name a few and may further affect the processing and rheological (flow) properties of the printing ink as well.
The benchmark for desired reaction rates of hydrocarbon-based compounds or VOCs is ethane. If a compound has a reaction rate with the hydroxyl radical and ultraviolet (xe2x80x9cUVxe2x80x9d) light that is faster than ethane, the compound reacts too close to the ground and consequently generates ozone and smog. Such compounds are defined as volatile organic compounds (VOCs). On the other hand, if a compound has a reaction rate that is slower than ethane, then the compound reaches higher into the atmosphere before reacting with the hydroxyl radical and UV light. In such instances, such compound does not contribute to the formation of ground based ozone and smog and therefore, is not considered a VOC.
The printing ink industry has a need to reduce VOC emissions as a result of state and federal health, safety and environmental laws and regulations, which affect printers. This has caused the industry to search for alternate chemicals, which would reduce the VOC levels and yet maintain or even enhance the properties of the ink. Another concern is the presence of hazardous air pollutants (HAPs) employed in printing inks which under the Federal Clean Air Act (FCAA) and Environmental Protection Agency (EPA), printers will perhaps be required to keep HAPs emission inventories.
Diethylene glycol, a common ingredient in aqueous letterpress printing inks, is an example of a VOC, while ethylene glycol is considered to be a VOC and a HAP.
In the United States, if a manufacturer emits air pollutants which must be controlled (such as VOCs or HAPs), the federal guidelines dictate adopting one of two courses of action to mitigate their emissions. The first is using engineering controls such as thermal or catalytic afterburners. This of course is a primary economic concern from the capital and operation perspective. The second is employing an alternate technology to reduce the amounts of VOCs and HAPs.
The present invention provides a printing ink composition comprising a resin and glycerine having less than 5 wt. % VOC and no HAPs.
The present invention also provides a printing ink composition additionally comprised of monoethanolamine, having less than 3 wt. % VOC and no HAPs.
The present invention further provides a method of preparing an aqueous letterpress or flexographic printing ink compositions containing resin and using glycerine to dissolve the resin, wherein said ink composition has less than 5 wt. % VOC and no HAPS.
Other objects and advantages of the present invention will become apparent from the following description and appended claims.
It has been found that the use of glycerine as a primary solvent for a printing ink resin imparts good flow properties and sufficient press stability to the ink without compromising on print quality and allows for the production of printing inks having no HAPs and a VOC content of less than 5 wt. %.
Preferably, the resin suitable for use in the present invention is maleic, acrylic or a combination thereof and the glycerine is preferably present at a concentration of about 25 to 80 wt. %, more preferably at 40 to 60 wt. %.
Commercial letterpress or flexographic water-washable printing inks often have a high VOC content. For example, Sun Chemical Corporation, Fort Lee, N.J. has available inks such as HydroSet, containing high VOCs.
HydroSet has a history of good printing performance and customer satisfaction. Therefore, a successful low VOC, HAPs free alternate to HydroSet would be required to exhibit the printing and end-use press performance the letterpress and flexographic printing industries have come to expect from HydroSet, as well as offering the equivalent manufacturing ease in production. Acceptable press performance requires that the printing ink stay wet (or xe2x80x9copenxe2x80x9d) on the printing press, but dry rapidly enough on the substrate being printed so as not to smear or xe2x80x9ctrackxe2x80x9d on the substrate. The prints must also offer the color strength and gloss equivalent to the standard established by HydroSet.
A number of solvent and resin combinations were evaluated as alternates to HydroSet. All except one, where the vehicle selected is dissolved in glycerine, failed in performance related either to its insufficient press stability or to poor print quality. Since glycerine is a no-HAPs and non-VOC material, the use of the glycerine in a vehicle as demonstrated below in the examples, provided the press stability and print quality equivalent to printing inks formulated with the xe2x80x9cstandardxe2x80x9d HydroSet.
Accordingly, under the present invention low VOC letterpress and flexographic printing inks for use in paper packaging, for example, (hereafter referred to as xe2x80x9cCompliant Inkxe2x80x9d) were formulated having a much lower VOC content than other commercially available letterpress and flexographic printing inks used in paper packaging. In addition, unlike many of the currently available printing inks for this particular application, the ink contained no HAPs materials. Lab evaluation of open time and press stability was made by observing the change in tack of the ink as it was run on an Inkometer; a machine with rotating rollers that simulates the action of rollers on a printing press. Ink transfer and print quality were evaluated with the use of a Vandercook proofing press.
Table 1 shows the composition for a typical non-Compliant water-washable letterpress or flexographic ink (HydroSet) used for paper packaging where the VOC content is 374.5 grams/liter (29.1%). The percentages expressed below are based on the total weight of the printing ink.
Table 2 shows a composition for a Compliant Ink where the VOC content is only 24.4 grams/liter (1.9%).
The invention is illustrated in even more detail by the following specific examples, but those of ordinary skill in the art will understand that the inveniton is not limited to the details thereof and that changes may be made without departing from the scope of the invention.